There is much discussion of a hydrogen powered economy in the distant future.
The obstacles are enormous but it will happen, we are told. My
question is: Is it possible to power a jet engine with anything other
than a petroleum derived fuel or a synthetic equivalent? If not, we
are unlikely to free ourselves from dependence on fossil fuels.

Hi monroe.
        Interesting point. Answers is yes.

It is possible to power a jet engine with other then fossil fuel.
Such jet engine is already used on some space vehicles: 

".. The challenge is reaching beyond the sophisticated fires that we
have now. The Space Shuttle Main Engines, for example, burn oxygen and
hydrogen stored in liquid form. Its Solid Rocket Boosters burn
aluminum and oxygen locked in a rubbery compound..."
http://science.nasa.gov/newhome/headlines/prop06apr99_1a.htm

Of course, those vehicles are carring not only Hydrogen, but Oxygen as well.

As long as you get the gases hot, really hot, they expand
and form a jet: 
http://www.factmonster.com/ce6/sci/A0859034.html

It is already being used: 
http://www.aerospaceweb.org/question/propulsion/q0170.shtml

It is topic of active research
http://aae.www.ecn.purdue.edu/v1/AAE/conferences/hydrogenperoxide.html

One word of caution though:
 Hydrogen economy still needs SOURCE of energy,
 Hydrogen is carrier - not a source - as explained e.g. in here:
http://answers.google.com/answers/threadview?id=456343

Hedgie

---

Clarification of Answer by hedgie-ga on 09 May 2005 19:31 PDT

Well Monroe

 You indeed should have worded your question differently, if you wanted 
 apology of a particular conviction, rather then an objective answer.

  I have stepped unwittingly on some ideological foot and your rating is
 reflection of that; It is not  fair:

 There is no 'but' between my answer and this:

"  But, over and above all that, hydrogen must be manufactured..."

I was not pushing 'hydrogen economy' or promoted alternative vs conventional
sources. I was answering an engineering question. Fact is that hydrogen CAN
be used to fuel a commercial jet. Economy of that and timing is a different 
question. If it will - is another questiuon. (I would bet on
intercontinental maglev in the distant future).

I have stated clearly in quoted GA:

Either source of energy, fossil, nuclear or solar, has to be combined with
the hydrogen technology to produce an sustainable, pollution free
future for our children.

Your statement:
"It has been estimated that to convert US cars to hydrogen fuel WITHOUT USING
FOSSIL FUELS would require more than one thousand nuclear power plants"

makes one wonder if the capacity of these plants enters the equation:
It will it need thousand of them, be they fusion, fission, breeders,
100 MW or 100 GW each?

Again, if you would be interested in the likely energy futures, you would 
to use a different wording.  I also wonder if you got that 'solar' in
the above given list of sources includes Solar Power Satellites
spacesolarpower.nasa.gov/ 
Again, that is another question.

hedgie-ga: Thanks for the interesting links, but I think the practical
answer is NO, which can be deduced from the info you supplied. In
fairness to you, I should have worded my question as it applies  to
commercial aviation. Scramjets and ramjets require speeds that cannot
be used for passenger jets. How would you get a fully loaded 747 to
Mach 5?  Space rocketry is not jet propulsion. As your GA link
explains, hydrogen contains much less energy per unit volume than jet
fuel. But, over and above all that, hydrogen must be manufactured.
Three of the four practical processes for it require, guess what,
petroleum products. The other, hydrolysis of water, requires
electrical power, which is mostly derived from, guess what again,
fossil fuels. Now, nuclear power plants could do it. It has been
estimated that to convert US cars to hydrogen fuel WITHOUT USING
FOSSIL FUELS would require more than one thousand nuclear power
plants.
Take a deep breath and hold it while this becomes reality.
monroe22

"Is it possible to power a jet engine with anything other than a
petroleum derived fuel or a synthetic equivalent?" - Just to your
information: The German navy has two brandnew full-size submarines
that are 100% hydrogen powered. If you can power a ship with hydrogen,
you can power a jet engine, too - it's only a matter of some
engineering work, but not of a "distant future".

Scriptor

scriptor-ga: Thanks for the interesting info about hydrogen powered submarines.
But I still maintain that commercial jet airplanes have no feasible
alternative to petroleum fuels. You have a touching faith in
technology, but are you an engineer? The submarine power plant turns
screws for propulsion. That engine is probably too bulky for aircraft,
but even if it is small enough, it would turn a propellor. But not to
worry, you say, it's only a matter of some engineering work to develop
a hydrogen powered jet. Read the links in hedgie-ga's answer and you
will be enlightened.
  Two submarines do not constitute a hydrogen economy. There are so
many obstacles to that, some seem insurmountable now. I grant you that
future technology may someday overcome them, but with present
knowledge, practical use of hydrogen for air or land transportation is
in the very distant future, if at all. Then we have the inherent
danger of storing hydrogen. Technology cannot alter its properties.
Hindenburg disaster, anyone?
monroe22

I agree with the rating of this answer and with Monroe22's purple box comment.
  The link to the space shuttle liquid propellent engines has
absolutely nothing to do with airbreathing turbine engines, other than
the fact that the shuttle engines use hydrogen.
  The link to scramjets - those are airbreathing engines but they have
no moving parts.  The question was specific towards gas turbine
engines.
  Hydrogenperoxide is used in some hybrid rocket engines.  This is one
instance where I believe it will never be applied to something like a
turbojet or turboprop.  Because it uses a solid and a gas.  (I was
fortunate to see a test firing of one of these last year)
  
If our fuel was Hydrogen and not a mix we would have to redesign the
entire engine.  Simply because we would be dealing with different
pressures, total pressures, total temperatures, temperatures,
densities, velocities, no doubt all kinds of new turbulence issues,
and of course very complex combustion etc.  So the whole combustor
would have to be totally redesigned along with the turbine,
compressor, not to mention all the things I have no understanding of
in the solid structure side of engineering.  I am not sure what kind
of heat tolerances this would require either.

Another issue I can think of right away would be how to store the
Hydrogen.  NASA has spent a long time trying to develop fuel (with a
little success) which will not explode in a major accident.  If we are
using Hydrogen gas or some other form to store the Hydrogen I worry
also of the possible explosions we might have one day.

I wonder if GE, Rollsroyce, or Pratt & W would be willing to scrap all
their current long term plans to go to this idea.  I doubt it, their
engines cost millions of dollers and all have design lifetimes of well
over 20 years!  Not to mention the hundreds of millions of dollers to
even design an engine.  I am sure that these companies have thought of
this very question and I do not believe they are considering it
because I have never heard anyone from those companies mention it.  A
few months ago I heard a talk from the director of GE aircraft engines
outlining their plans for the next 10 years, and nowhere in those
plans did I hear the words "hydrogen fuel source".  If they were going
to do this it would not be for another 20 years (in my opinion) before
they hit the market for Boeing or Airbus etc to buy up.

I do like the idea, perhaps it represents a new set of challenges for
us in the future.

I forgot to mention NACA's work on hydrogen gas-turbine engines.  My
appologies.  however this research was done on engines of that era,
just a disclaimer. :)

http://www.hq.nasa.gov/office/pao/History/SP-4404/ch6-8.htm

saem_aero-ga:  Many thanks for your astute comments. For what is
worth, I believe that the alternate energy enthusiats are completely
divorced from reality. They are completely ignorant of the laws of
thermodynamics, which can be summed up in a short sentence, to wit: 
THERE IS NO FREE LUNCH. Got that, alternate energy people? Repeat:
THERE IS NO FREE LUNCH. Now, if that is beyond your comprehension,
allow me to inform you that you are totally hopeless.
monroe22

Just to chime in here for a moment. I will try and comment only on the
hydrogen issue.

Hydrogen gas has to be, for the most part, derived from some other
hydrocarbon source, like methane.  You can also produce hydrogen gas
from a reverse of the process that happens in a fuel cell (i.e. from
water). But, of course, you need as much energy in producing a set
volume of hydrogen gas as you get out of it. This is basic chemistry.

Now, given this obvious limitation, the question becomes: Is it
feasible to produce hydrogen when hydrogen itself is costly to
produce. While we might be tempted to say 'no' the answer may be 'yes'
if certain conditions are met.

First, it is possible to extract hydrogen using a clean and efficient
source of energy, such as wind or solar power. This hydrogen could
then be transferred to a container that is safe and which carries
enough hydrogen fuel for whatever needs exist.  Of course, so far the
problem is that 1. Safety is still a major PR concern (along the lines
of the 'Hindenburg' disaster- even though hydrogen gas is actually
pretty safe by itself). 2. Containers haven't been developed that
correct the problem of bulkyness. For example, applications in small
electronics are limited by the fact that a fuel cell battery providing
enough Watt-hours as a regular battery is likely to be bulky. But this
problem is being worked on.

The hydrogen fuel cell offers a number of distinct advantages. By
itself, the fuel cell is highly efficient and clean. People have said
that fuel cells are really not 'clean' because they rely upon
nonrenewable sources for the production of hydrogen. This is simply
not true: solar, wind, hydroelectric, and even nuclear power can be
used to produce hydrogen. I'm not sure why it is absolutely necessary
to rely on nuclear energy alone as opposed to other sources, as one
person commented. In effect what hydrogen fuel cells do is they
transfer clean energy from one source to another, with high
efficiency.  One of the biggest problems with fossil fuels today is
that they are used inefficiently. Even if hydrogen were produced by
using nonrenewable fuels, society would still be better off because
that energy would be used much more efficiently than combustion
engines.

Now, can hydrogen fuel cells be used in airplanes and the like?  If we
are talking about the distances and weight required by jetliners
today, the answer most likely, is no.

But trains are already being developed that run on hydrogen fuel
cells, as well as cars.  If the basic idea is to wean society off of
nonrenewable fuels, then slowly switching to a hydrogen economy
certainly helps. My hunch is that public transportation will be the
first major area of this 'conversion'.  Unfortunately, America has
never gotten itself off the habit of relying on the highly inefficient
combustion engine in cars and SUV's.

America, so advanced as it is in technology, stands as a backwater
nation when it comes to improvements to public transportation, even
though public transportation can deliver immense benefits in terms of
energy efficiency and cleanliness. The Bush Administration is quick to
point to the need for more oil drilling, but makes short mention of
the advantages of renewable energy sources. And ironically, at a time
when gas prices are high, the Bush Administration is considering a cut
to Amtrak while SUV's receive tax breaks.  Only in America, folks.

af40-ga
          I want to thank you for adding a sensible comment to what
otherwise looks like pub brawl about FREE LUNCH (and no beer?).

I just want to comment on your 

"I'm not sure why it is absolutely necessary
to rely on nuclear energy alone as opposed to other sources, as one
person commented" 

Nuclear is not the only source. My GA reference in the answer lists several:

"....... To make hydrogen from water takes energy. Hydrogen is a carrier,
similar to a battery or a transmission line, not a source.
For new sources, to replace  current fossil fuels we have very few options :
some renewable sources, such as tides, eg
http://www.baycrossings.com/Archives/2002/09_October/tidal_energy.htm
but mostly SPS and fusion. Both are being pursued ..."


The stats on what is being used, available and feasible are on the web, e.g. at 
http://www.eia.doe.gov/emeu/iea/
 The only problem with these is that they measure consumption in
  (Quadrillion (10 to the power of 15) Btu) or quads per year 

World is using about 21E12 Watts - that is not easy to replace.

The breakdown by consumption is here: 
http://energy.cr.usgs.gov/energy/stats_ctry/Stat1.html

     Transportation 25.04 quads - 27%  of US total
      ( I suppose that can be also expressed as 1000 nuclear plants :-)
etc

while I agree with you that
The Bush Administration policies are -- well -- peculiar

what I really do not get is this: 
1) why 'they' cannot use SI units, like Watts and TerraWatts
     insted of quads and BTU and  'power plants'.
     Do they want to confuse the inumerate?
2) Why do peaple waste so much intellectual (and screaming) energy
   arguing when the selection of fuel depends on cost and cost depends
on availability.
    Due to the fact of 'the peak-oil', which will happen wheather or not will 
    Bush administration succeed in  'democratizing' Middle East countries
    and drilling Alaska full of holes, fossil fuel will be more and more scarce
    and therefore more and more expensive. 
    So, what's the point?

I dont think that hydrogen will ever be used in commercial aircraft as
the cost of manufacturing large light weight hydrogen fuel tanks would
be to high.
I have done a lot of studying on gas turbine engines and I cant see
why they could not be made to run on a fuel like bio-diesel.
The US Army uses gas turbine generators and they will run on diesel or
paraffin (kerosene in US), I do not know if they have ever tried
running the engine on bio-diesel to see what happens.
Has anyone ever tried to run a turbine engine on bio-diesel?

In answer to the original question:

Jet engines can be run on hydrogen.
Jet engines have been run on hydrogen.
Work is in progress to produce hydrogen powered jet airliners which
may start flying by 2010.

The engine itself requires little modification.
The hydrogen must be carried as liquid but this is a soluble problem.
The explosion and fire hazards of hydrogen are less than those for
conventional aviation fuel - though public perception imagines the
opposite.

A Russian Tupolev TU-154 had one of its three engingines converted to
hydrogen in in 1988.

This was followed by a joint venture between Tupolev and
DaimlerChrysler Aerospace/Airbus in the early 1990s.

This in turn was followed by a multinational european project called cryoplane.
  


For more information try these links or just google cryoplane.

http://www.bl.uk/collections/patents/greenaircraft.html

http://www.h2hh.de/downloads/Westenberger.pdf

Actually those German submarines were built during WW2. Type 29, I
believe?  They used Walter engines that mixed hydrogen perxide and
water:

http://aae.www.ecn.purdue.edu/v1/AAE/conferences/hydrogenperoxide.html

I agree with the posters that hydrogen is simply an energy storage
system that still has to be "charged" as it were: 
http://www.01planet.info

And some aircraft were able to use hydrogen in the early 20th century:
http://www.air2air02.info